Semi-trucks generally comprise of a tractor and a trailer. For safety purposes federal and state regulations generally require that the loads carried in the trailers meet certain weight requirements. The weight requirements apply to the steers, the drives and the tandems of the trailer. It is well known in the art that the positioning of the trailer with respect to the tandems in the rear of the trailer affects the weight at all three locations on the trailer. As such semi-truck trailers are generally constructed to slide back and forth over the tandems of the trailer until the proper position is achieved and then locked into that position. The trailer comprises two parallel rails, fastened underneath the trailer and are fitted over corresponding rails on the tandems. The trailer rails include a series of pinholes positioned to engage extendable pins located on the tandems through holes in the tandem axle rails. Two or four pins systems are generally employed to lock the trailer and tandems together. In their use the pins are retracted to permit the trailer to slide back and forth over the tandems and are extended to lock the trailer to the tandems when the proper position is achieved. The mechanism used to extend and retract the pins is usually located on the tandems and controlled by a locking pin handle or lever wherein the displacement of the locking pin handle or lever simultaneously moves all of the pins.
The pin holes in the trailer rails are located so they can correspond to the locations of the pins such that lining up one of the holes on the trailer rail with a locking pin on one side of the tandems will simultaneously line up a hole on the trailer rail on the opposing side of the trailer with a locking pin on the other side of the tandems.
One of the main problems associated with positioning the trailer in the proper position over the tandems axle in the desired location is that the driver moving the tractor cannot see the relative position of the trailer with respect to the tandems at the back of the trailer. More specifically, once a desired locking pin hole in the trailer rails has been selected, the driver working alone must guess and move the tractor to slide the trailer until he/she thinks the correct position has been obtained. The driver then has to get out of the tractor to verify that the correct position has been obtained. The aforementioned steps are repeated until the correct position has been acquired. Even with experience driver, most drivers have to make several trips climbing in and out of the tractor before positioning the trailer over the tandems at the selected location. It is not unexpected to take around 20-30 minutes or more for an experience driver to position the trailer in the desired position over the tandems axle.